IIRC optimal will be around 37* from the ground to counter air resistance. It’s been a while since I’ve had to integrate the projectile motion equations…
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But 90 degrees would make a better video…
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I’ve been researching the sling/pouch and subsequent tuning. I’ll describe what I found, and if the team is already past this point, then I apologize in advance. Not trying to second guess here …
POUCH DESIGN:
It seems that @Brandon_Green open webbing pouch is a good idea. According to Urban Siege, and their world championship quest, “big solid pouches tend to act as pretty good sails, slowing down the launch speed, and thus killing range. Therefore, solid pouches usually are not used for launching anything rather large, such as a pumpkin (like the 8-10 pounders used in competition).” It clearly needs to cradle the pumpkin, so again … good design on the webbing prototype.
TWO-PART SLING/POUCH:
The few pictures I could find suggest that the pouch and the sling “rope” (sorry - don’t know what else to call it) are frequently two separate pieces. This one from [Yankee Siege] (https://www.pinterest.com/pin/79587118385357648/) shows something very similar to our webbing prototype, using tubular webbing as the “rope”.
I may have misunderstood, but I think we had considered having our pouch webbing extend out and be the “rope” that connects it to the arm, but that would make it difficult to adjust length. We would need a discrete pouch/sling for each projectile size/trajectory combination.
I recommend we find a way to have a separate pouch to attach to our sling “rope”, if we haven’t already done this. This also makes installation easier if we have a field failure of the pouch.
ADJUSTABLE LENGTH:
The larger/more elaborate trebs have a way to adjust the length of the sling to “tune” for different sizes of projectiles/trajectories. This is compatible with the separate sling/rope design concept.
I found this interesting photo. It shows a pouch that has a movable position along a rope. They pass the rope through the fabric sling, which IMO doesn’t seem to be a good idea because of both the fragility and the aerodynamics of a fabric sling. I like the idea, but I’m not sure how we would implement that with a pouch on D-rings.
SLING LENGTH:
Opinions differ on the optimal length of the sling, but these should provide us a starting point:
• The length of the sling is equal to the length of the long arm of the beam (on the payload side) (attributed to Donald B. Siano, in his analysis of trebuchet physics (Trebuchet Mechanics, March 28, 2001).
- The general ratio to start at is a sling length (arm connection to tip of pouch) 80% the length of the throwing arm. Longer length slings have a lower angle of release, good for line drives … Shorter lengths will result in a higher angle of release, best for lobbing projectiles over tall objects.
There is some opinion that higher trajectories (i.e., shorter sling) give more precise shots, in which case an adjustable sling might be useful for the accuracy category. This conceptually makes sense - in the case of a vertical shot the variation in the flight path would be mostly in the Z-dimension so the X,Y variation would be less.
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I volunteered to sew up the pouches, and as you can probably tell, I’m chomping at the bit to get started on this. But I don’t want to do this until we have a little better idea exactly what we’d like to make. I’d love to find a way to test the webbing prototype to see if it’s suitable as a pouch. I’m optimistic that if we make the pouch separate from the sling “rope” then I could be working on the pouches, which I suspect will take longer to make than the “rope”.
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I think the following would work, not shown is the detail of how it attaches to base in a removable way, there would be 2 pieces of steel angle coming out at a 45 degree angle from the base, and a single bolt would go through the steel angle and a hole drilled through the square tubing, so the legs can pivot on one axis. Also not shown is there would be a foot contacting the ground that connects to the tube the same way, with a bolt going through the square tubing.
The end of each foot is connected via a ratchet strap to the base, and there is a piece of steel angle connecting two legs together on an end.
Parts list
4x 60" long, 2"x2" 14 gauge steel tube
4x ratcheting tie down straps
2x 72" long, 1" x 1/8" steel angle (connects two feet together rigidly)
4x 12" long, 2" x 1/8" steel angle (support to base mount)
4x 12" long, 2" x 1/8" steel angle (support to foot mount)
8x 12" long 2" x 1/8" steel angle (foot)
(and miscellaneous fasteners found around dms)
Materials order
4x 5’ 2" x 2" 14ga square tube, $46
2x 8’ 2" x 2" 1/8 steel angle, $30.60
2x 6’ 1" x 1" 1/8 steel angle, $18.00
$104.06
But looking at expenses so far
Sep 5, 2016 Westlake Hardware ‡2 COMMITTEES:PR $10.94
Sep 6, 2016 The Home Depot ‡3 COMMITTEES:PR Trebuchet $60.62
Sep 19, 2016 SERVICECAST ‡8 COMMITTEES:PR Trebuchet $71.12
Sep 20, 2016 Amazon ‡5 COMMITTEES:PR Trebuchet $16.35
Sep 20, 2016 Amazon ‡2 COMMITTEES:PR Trebuchet $37.50
Sep 20, 2016 Amazon ‡4 COMMITTEES:PR Trebuchet $45.89
Sep 20, 2016 Amazon ‡3 COMMITTEES:PR Trebuchet $54.32
Sep 20, 2016 Amazon ‡1 COMMITTEES:PR Trebuchet $75.03
Sep 20, 2016 Metals 4 U Inc Dallas ‡7 COMMITTEES:PR Trebuchet $646.83
Sep 22, 2016 The Home Depot ‡6 COMMITTEES:PR Trebuchet $34.88
Sep 25, 2016 Amazon ‡2 COMMITTEES:PR Trebuchet $8.54
Sep 25, 2016 Harbor Freight Tools 357 ‡4 COMMITTEES:PR Trebuchet $98.12
Sep 25, 2016 Metals4uonline ‡3 COMMITTEES:PR Trebuchet $79.08
Sep 25, 2016 Westlake Hardware ‡5 COMMITTEES:PR Trebuchet $25.96
Sep 27, 2016 Amazon ‡5 COMMITTEES:PR Trebuchet $21.92
Sep 27, 2016 Amazon ‡7 COMMITTEES:PR Trebuchet $33.77
Sep 28, 2016 Amazon ‡6 COMMITTEES:PR Trebuchet $3.24
Sep 29, 2016 The Home Depot ‡2 COMMITTEES:PR Trebuchet $95.80
Sep 30, 2016 The Home Depot ‡1 COMMITTEES:PR Trebuchet $26.02
Oct 2, 2016 The Home Depot ‡1 COMMITTEES:PR Trebuchet $20.97
We have spent $1,466.90 of our $1,500 budget, so I can either spend auto money on this or start asking for donations
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I’ll toss in a hundo. 
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The weights turned out fairly consistent in mass, all around 110-115 pounds, looks like I overshot the target by 20% and we will have a max of 1,200 pounds including the weight axle
Also did some more welding on the end of the arm, this is where winch connects to to lift the 1,200 pounds
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Sorry I failed to get down there Wednesday.
Your welding looks great from here though!
And that isn’t saying anything about how nixe your weights turned out.
Well done! What remains to be done now?
Heat / relief welds on outside of uprights
Remove temporary spacers
Test motion of arm
Weld arm end cap and release pin and angle adjuster
Assemble trigger assemblies and weld to top
Design and weld winch mount
Design and build spring loaded trigger (remote end)
Order, pickup, build detachable legs
Get new spanner bushing for new arm pivot wheels and replace gray wheels
Design and build secondary safety
Final welding of rail tracks
Attach test sling
Test fire with min weight
Test fire with half weight
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I am talking to a fellow right now who could help me get my O2 tank refilled and then I will be able to heat up the sides of the trebuchet to try and draw it back to dimension.
Might be next week though. If we cannot wait that long we could rent a rig or put out a request to borrow one.
If time is of the essence, welding just to grind off the welds is going to be very labor intensive.
Hopefully he needs to draw in a direction where the welds can be ignored.
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That would be ideal, but I do think he wanted them where the counterweights were going to slide, which demands a flush surface.
If I am wrong and we can get away with it I would be thrilled to do a surface weld on it.
We could wait for the o2, but I’m not good at waiting, if we run out of other things to do on sunday can do the surface welding then grinding it smooth
What about running beads just around the corners from the side we need to bend towards? Any chance of drawing it in that way and avoiding the need to grind as completely/carefully?
Tried to draw here, red being warp direction (not to scale), it is warped some in both dimensions, both of the faces in picture will have something sliding over it. Was thinking of running bead where the green lines are.
I was just talking to my Foreman about our plight and showed him the picture.
He said, “can any of your friends get the bottle refilled?”
I have it with me right now and will be near the space this very evening. If someone could get it filled for me tomorrow morning. Save the receipt and I will repay you Saturday afternoon once I get out of work.
What do you think.
Is this the reason that the wide cross-bar thingy isn’t level?
I may be confused.
I thought that the warping was really only evident in the vertical elements.
If only I had gas…I used to straighten I beams with heat like that.
Well, my opinion does not constitute the official opinion … but today I was standing in the shop and looking at the treb, straight on or fairly close. The arm really does not look level.
And before someone says that it’s just the angle of the photograph … I viewed it in person. I didn’t judge it from this photograph. I was just lucky that @Brandon_Green had uploaded a relevant photo.
I know the floor may not be level, but this looked pretty far off. I didn’t have any measuring tools with me to check whether it’s square / perpendicular / straight, etc. so it might be OK.
But I think someone who knows these things might ought to look at it. And even if it’s not “level”, it might not matter, either.
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Will have to double check that arm pivot axle that the two wheels are mounted on is parallel to the weight axle (4’ steel rod). For that part was mainly depending on the carbide hole saw through the arm beam drilled on bridgeport to align the arm pivot bushing to the arm while welding.
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It always pays to have a second pair of eyes see your work.
I will often overlook my own mistakes.
Keep on double checking!